1. Field of the Invention
The present invention relates to a signal processing device that processes an input audio signal, as well as a method and program therefor.
2. Description of the Related Art
When conducting sound reproduction using a speaker on the basis of an audio signal, it is known that in sound reproduction using a small speaker, for example, ample bass reproduction cannot be realized due to limitations imposed by the physical volume of the speaker.
FIG. 25 shows a comparison between the frequency characteristics (i.e., frequency-amplitude characteristics) of a large speaker and a small speaker. In the case of the large speaker indicated in FIG. 25A, amplitude drop at the lower frequency bound of the figure (50 Hz) cannot be seen, while in the case of the small speaker indicated in FIG. 25B, it can be seen that the amplitude is dropping at frequencies below 200 Hz.
Various methods for improving the reproduced sound of bass components with small speakers have been proposed for some time. One of these involves boosting the bass component. Typically, bass component signals are not completely absent from playback, even with small speakers. Consequently, reproduced sound can be obtained at attenuated volumes compared to those of a large speaker, as shown in FIG. 25B. Thus, by raising the gain to boost the bass component, reproduced sound can be obtained that extends to the bass region.
In addition, another technique is known wherein harmonic waves of the bass signal are added. More specifically, the bass component of an audio signal is extracted and processing to generate harmonic waves is performed thereon (using full-wave rectification, for example). In so doing, a harmonic signal of the bass component is generated. Subsequently, the harmonic signal is added to the audio signal. By conducting such processing, the presence of the harmonic waves causes the listener to perceive that a bass signal is present, even if the bass signal is not actually reproduced. This phenomenon is typically known as the “missing fundamental”.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. H11-509712 discloses background art related to the above.